From what I've seen you don't normally need too much - a few lines each on appearance, personality and history / where they've come from should be enough.

If you use the search bar at the top of the main page to search for 'permission request' you should be able to check out what sort of information people have included in requests before, and whether they were successful with that or not.

One to three paragraphs sounds about right to me. I'd say lean toward the longer side if your writing sample isn't about your agents. Like the page says, we just need enough to tell that they aren't overpowered, trajeck, or otherwise speshul. How much that takes can vary.

More questions is fine. Try to ask them in this thread as long as you can, though.

~Neshomeh